In space exploration, one of the significant problems to deal with is the ever increasing amount of space debris. The problem of space debris overshadows the natural meteoroid activity for a number of reasons. Man-made debris tends to be more dense (metals, etc.) than natural debris (rock, etc.), therefore, man made debris poses more damage potential. Also, man made space objects can have extremely long orbital life and are subject to collisions while traveling at high velocities. The collision impact of such space debris, in turn, generate smaller debris fragments all of which constitute contaminates in space. The small size debris fragments have a particulate size of 0.01 cm to 1.0 cm and at hypervelocities can cause damage to spacecraft or personnel upon impact. It is generally accepted that anything below about 10 cm isn't trackable, therefore, these small particles are not trackable and constitute an unknown hazard to space operations.
In the context of the present invention the term "hypervelocity" refers to velocities in excess of 2 KM/sec and the term "projectiles" refers to both man-made debris and naturally occurring meteoroids.
Existing solutions to protect space vehicles and personnel from projectiles include "Whipple Bumper" shields which consist of a system of thin aluminum sheets separated by discrete spacings so that hypervelocity projectiles are ablated upon penetration of the sheets. Other materials such as ceramic fabrics or metallic meshes can be substituted for the aluminum sheets.
In a "Whipple Bumper" shield, the parameters of the aluminum sheet thickness and layer spacing define the effectiveness of the shield. For example, a shield that would protect against a 2 mm projectile travelling at 8 km/sec is ineffective against a 5 mm projectile travelling at 2.5 km/sec. Thus, designing shields for a range of projectile sizes, travelling at between 2 and 20 km/sec, becomes a difficult problem.
Additionally, "Whipple Bumper" shields have several other limitations in that:
5 1. aluminum sheets are heavy, resulting in high launch cost penalties; PA1 2. aluminum sheets are opaque so that, this type of shield cannot be used to protect windows, face shields, or solar arrays; PA1 3. rigid sheets must be custom-designed to cover spherical, or otherwise configured structural shapes; PA1 4. sharp metallic edges pose a hazard to personnel working on or near the shields, particularly in an EVA situation; PA1 5. they require rigid mounting hardware and cannot easily be retrofitted to in-place structures; PA1 6. rigid mounting hardware increases both material and launch costs; PA1 7. many impacts on "Whipple Bumpers" cannot be detected without very close visual inspection; on orbit a costly inspection program is needed to ensure timely replacement of the shields; PA1 8. whipple bumpers are "directional". In order to be most effective, projectile must impact at right angle; and PA1 9. on impact, aluminum whipple bumpers produce "ejecta", that is, more metallic projectiles added to the debris environment.
Variations on the "Whipple Bumper" shield, particularly a ceramic fabric shield, have addressed some of the limitations. Weight and thus cost can be decreased; mounting is simplified; and sharp edges can be eliminated; however, most of the other limitations remain.
In military applications, "reactive" armor is sometimes used to protect vehicles and structures from high velocity projectiles. Such armor mechanically reacts upon impact and redirects impact energy away from the element to be protected. "Reactive" Armor has many of the same limitations as the "Whipple Bumper" shield: it is opaque, it cannot be easily retrofitted to in-place space structures, and it may pose a safety hazard to personnel working on or near it in that it also produces secondary projectiles. Reactive armor is also undesirable for civilian use due to the safety issues involved in transporting the dangerous chemical compounds required; the classified nature of most reactive armor precludes its use for international civilian endeavors; and propulsion issues related to armor reaction can be complicated in a space environment.
It can be appreciated that a simpler, lightweight impact shocking system can have considerable utility as a shield for hypervelocity projectiles.